Yes, you can continue having plantains during pregnancy. As per an article in the American Botanical Council, there is no harm in having plantains when you are expecting. Moreover, plantains are rich in dietary fiber which helps in digestion and relieves constipation. Hence, they can be a good addition to your pregnancy diet.
Taking common medicines during pregnancy, a summary of NHS UK guidelines
You should definitely check with your doctor before taking any medication during pregnancy. Even for medication you were already on at the time of getting pregnant, now needs to be approved by your doctors as